The Northern Brown Argus is restricted in the UK to northern Britain where it is very localised occurring in discrete colonies on generally south-facing calcareous grassland slopes where its main foodplant Rockrose (Helianthemum nummularium) grows. (For further details on this species see http://www.butterfly-conservation.org/).

Status details : Status since 1979 is Rapid decline with a decrease of -59.6%Status over the last 20 years is Rapid decline with a decrease of -48.0%Status over the last 10 years is Stable with a decrease of -2.8%

Log collated index plot

This chart shows the index of abundance (LCI = Log Collated Index) over time. It shows fluctuations in
populations from year to year, and is scaled so that the average index over the whole series is equal to 2
(horizontal line). For greater detail about how this index is derived, click on the green question mark above.

Trend description :This UK BAP species has significantly declined since monitoring began. Although this decline has slowed down in more recect years, it remains a species of conservation concern and is not significantly increasing on any of the transects on which it has been recorded. Sites in Lancashire and Cumbria such as Warton Crag still regularly record three figure indices for Northern Brown Argus.

Phenology plot

Phenology plot

This chart shows the average number of butterflies seen on transects between Arpil and October across all sites (fitted values from a Generalised Additive Model). The blue line gives average counts over the full BMS series (1976 to date) and the red line gives the average for the last year.

This map shows symbols for the mean abundance at transect sites, with the colour of the symbol reflecting the level of abundance. Means are over all years. Grey background squares are the occupied cells as shown by the Butterflies for the New Millenium over the previous ten year period.

Coverage

In total, Northern Brown Argus has been recorded from 198 transects in the Butterfly Monitoring Scheme. Of these, annual indices of abundance have been calculated from 50 sites, with an average index of 34 individuals per site.

For 24 of these sites, Northern Brown Argus has been recorded well enough to calculate annual indices of abundance in more years, allowing trends to be calculated.

In 2017, 1087 individuals were recorded from 27 sites, producing annual indices at 22 of these.

This map shows the trend in abundance at particular transect sites for which data has been received within the last five years. Trends (increasing, declining or stable) are assessed at sites where the species has more than five years of annual index data. Use the option boxes below to view plots for individual sites.